DICHLORODIPHENYL TRICHLOROETHANE

DDT is the generally used abbreviation for the compound which has been given the oﬃcial name of dicophane. It was ﬁrst synthesised in 1874, but it was not until 1940 that, as a result of research work in Switzerland, its remarkable toxic action on insects was discovered. This work was taken up and rapidly expanded in Great Britain and the USA, and one of its ﬁrst practical applications was in controlling the spread of TYPHUS FEVER. This disease is transmitted by the louse, one of the insects for which DDT is most toxic. Its toxic action against the mosquito has also been amply proved, and it thus rapidly became one of the most eﬀective measures in controlling MALARIA. DDT is toxic to a large range of insects in addition to the louse and the mosquito; these include houseﬂies, bed-bugs, clothes-moths, ﬂeas, cockroaches, and ants. It is also active against many agricultural and horticultural pests, including weevils, ﬂour beetles, pine sawﬂy, and most varieties of scale insect.

DDT has thus had a wide use in medicine, public health, veterinary medicine, horticulture, and agriculture. Unfortunately, the indiscriminate use of DDT is potentially hazardous, and its use is now restricted or banned in several countries, including the United Kingdom.

The danger of DDT is that it enters the biological food chain with the result that animals at the end of the food chain such as birds or predators may build up lethal concentrations of the substance in their tissues.

In any case, an increasing number of species of insects were becoming resistant to DDT. Fortunately, newer insecticides have been introduced which are toxic to DDT-resistant insects, but there are doubts whether this supply of new insecticides can be maintained as insects develop resistance to them.